Methods of forming gate structures for transistor devices for CMOS applications

ABSTRACT

One method for forming replacement gate structures for NMOS and PMOS transistors includes performing an etching process to remove a sacrificial gate structure for the NMOS and PMOS transistors to thereby define NMOS and PMOS gate cavities, depositing a gate insulation layer in the gate cavities, depositing a first metal layer on the gate insulation layer in the gate cavities, performing at least one process operation to form (1) an NMOS metal silicide material above the first metal layer within the NMOS gate cavity, the NMOS metal silicide material having a first amount of atomic silicon, and (2) a PMOS metal silicide material above the first metal layer within the PMOS gate cavity, the PMOS metal silicide material having a second amount of atomic silicon, and wherein the first and second amounts of atomic silicon are different, and forming gate cap layers within the NMOS and PMOS gate cavities.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the present disclosure relates to the manufacture ofsemiconductor devices, and, more specifically, to various novel methodsof forming gate structures for transistor devices for CMOS applicationsand various novel integrated circuit products that contain suchtransistor devices.

2. Description of the Related Art

The fabrication of advanced integrated circuits, such as CPU's, storagedevices, ASIC's (application specific integrated circuits) and the like,requires the formation of a large number of circuit elements in a givenchip area according to a specified circuit layout, wherein so-calledmetal oxide semiconductor field effect transistors (MOSFETs or FETs)represent one important type of circuit element that substantiallydetermines performance of the integrated circuits. The transistors aretypically either NMOS (NFET) or PMOS (PFET) type devices wherein the “N”and “P” designation is based upon the type of dopants used to create thesource/drain regions of the devices. So-called CMOS (Complementary MetalOxide Semiconductor) technology or products refers to integrated circuitproducts that are manufactured using both NMOS and PMOS transistordevices.

Field effect transistors, whether an NMOS or a PMOS device, typicallyinclude a source region, a drain region, a channel region that ispositioned between the source region and the drain region, and a gateelectrode positioned above the channel region. Current flow through theFET is controlled by controlling the voltage applied to the gateelectrode. For an NMOS device, if there is no voltage (or a logicallylow voltage) applied to the gate electrode, then there is no currentflow through the device (ignoring undesirable leakage currents, whichare relatively small). However, when an appropriate positive voltage (orlogically high voltage) is applied to the gate electrode, the channelregion of the NMOS device becomes conductive, and electrical current ispermitted to flow between the source region and the drain region throughthe conductive channel region. For a PMOS device, the control voltagesare reversed. Field effect transistors may come in a variety ofdifferent physical shapes, e.g., so-called planar FET devices orso-called 3D or FinFET devices.

For many decades, planar FET devices were the dominant choice for makingintegrated circuit products due to the relatively easier manufacturingmethods that are used to form such planar devices as compared to themanufacturing methods involved in forming 3D devices. To improve theoperating speed of planar FETs, and to increase the density of planarFETs on an integrated circuit device, device designers have greatlyreduced the physical size of planar FETs over the years. Morespecifically, the channel length of planar FETs has been significantlydecreased, which has resulted in improving the switching speed of planarFETs. However, decreasing the channel length of a planar FET alsodecreases the distance between the source region and the drain region.In some cases, this decrease in the separation between the source andthe drain regions makes it difficult to efficiently inhibit theelectrical potential of the source region and the channel from beingadversely affected by the electrical potential of the drain region. Thisis sometimes referred to as so-called short channel effects, wherein thecharacteristic of the planar FET as an active switch is degraded.

As noted above, in contrast to a planar FET, a so-called 3D or FinFETdevice has a three-dimensional (3D) structure. More specifically, in aFinFET, a generally vertically positioned fin-shaped active area isformed in a semiconductor substrate and a gate structure (gateinsulation layer plus the gate electrode) is positioned around both ofthe sides and the upper surface of the fin-shaped active area to form atri-gate structure so as to use a channel having a three-dimensionalstructure instead of a planar structure. In some cases, an insulatingcap layer, e.g., silicon nitride, is positioned at the top of the finand the FinFET device only has a dual-gate structure. Unlike a planarFET, in a FinFET device, a channel is formed perpendicular to a surfaceof the semiconducting substrate so as to reduce the physical size of thesemiconductor device. Also, in a FinFET, the junction capacitance at thedrain region of the device is greatly reduced, which tends to reduce atleast some short channel effects. When an appropriate voltage is appliedto the gate electrode of a FinFET device, the surfaces (and the innerportion near the surface) of the fins, i.e., the substantiallyvertically oriented sidewalls and the top upper surface of the fin,become a conductive channel region, thereby allowing current to flow. Ina FinFET device, the “channel-width” is approximately two times (2×) thevertical fin-height plus the width of the top surface of the fin, i.e.,the fin width. Multiple fins can be formed in the same foot-print asthat of a planar transistor device. Accordingly, for a given plot space(or foot-print), FinFETs tend to be able to generate significantlystronger drive currents than planar transistor devices. Additionally,the leakage current of FinFET devices after the device is turned “OFF”is significantly reduced as compared to the leakage current of planarFETs due to the superior gate electrostatic control of the “fin” channelon FinFET devices. In short, the 3D structure of a FinFET device is asuperior MOSFET structure as compared to that of a planar FET,especially in the 20 nm CMOS technology node and beyond.

For many early device technology generations, the gate structures ofmost transistor elements has been comprised of a plurality ofsilicon-based materials, such as a silicon dioxide and/or siliconoxynitride gate insulation layer, in combination with a polysilicon gateelectrode. However, as the channel length of aggressively scaledtransistor elements has become increasingly smaller, many newergeneration devices employ gate structures that contain alternativematerials in an effort to avoid the short channel effects which may beassociated with the use of traditional silicon-based materials inreduced channel length transistors. For example, in some aggressivelyscaled transistor elements, which may have channel lengths on the orderof approximately 10-32 nm or less, gate structures that include aso-called high-k dielectric gate insulation layer and one or more metallayers that function as the gate electrode (HK/MG) have beenimplemented. Such alternative gate structures have been shown to providesignificantly enhanced operational characteristics over the heretoforemore traditional silicon dioxide/polysilicon gate structureconfigurations.

Depending on the specific overall device requirements, several differenthigh-k materials—i.e., materials having a dielectric constant, ork-value, of approximately 10 or greater—have been used with varyingdegrees of success for the gate insulation layer in an HK/MG gateelectrode structure. For example, in some transistor element designs, ahigh-k gate insulation layer may include tantalum oxide (Ta₂O₅), hafniumoxide (HfO₂), zirconium oxide (ZrO₂), titanium oxide (TiO₂), aluminumoxide (Al₂O₃), hafnium silicates (HfSiO_(x)) and the like. Furthermore,one or more non-polysilicon metal gate electrode materials—i.e., a metalgate stack—may be used in HK/MG configurations so as to control the workfunction of the transistor. These metal gate electrode materials mayinclude, for example, one or more layers of titanium (Ti), titaniumnitride (TiN), titanium-aluminum (TiAl), titanium-aluminum-carbon(TiALC), aluminum (Al), aluminum nitride (AlN), tantalum (Ta), tantalumnitride (TaN), tantalum carbide (TaC), tantalum carbonitride (TaCN),tantalum silicon nitride (TaSiN), tantalum silicide (TaSi) and the like.

One well-known processing method that has been used for forming atransistor with a high-k/metal gate structure is the so-called “gatelast” or “replacement gate” technique. The replacement gate process maybe used when forming planar devices or 3D devices. FIGS. 1A-1Dsimplistically depict one illustrative prior art method for forming anHK/MG replacement gate structure using a replacement gate technique. Asshown in FIG. 1A, the process includes the formation of a basictransistor structure above a semiconducting substrate 12 in an activearea defined by a shallow trench isolation structure 13. At the point offabrication depicted in FIG. 1A, the device 10 includes a sacrificialgate insulation layer 14, a dummy or sacrificial gate electrode 15,sidewall spacers 16, a layer of insulating material 17 and source/drainregions 18 formed in the substrate 12. The various components andstructures of the device 10 may be formed using a variety of differentmaterials and by performing a variety of known techniques. For example,the sacrificial gate insulation layer 14 may be comprised of silicondioxide, the sacrificial gate electrode 15 may be comprised ofpolysilicon, the sidewall spacers 16 may be comprised of silicon nitrideand the layer of insulating material 17 may be comprised of silicondioxide. The source/drain regions 18 may be comprised of implanteddopant materials (N-type dopants for NMOS devices and P-type dopants forPMOS devices) that are implanted into the substrate 12 using knownmasking and ion implantation techniques. Of course, those skilled in theart will recognize that there are other features of the transistor 10that are not depicted in the drawings for purposes of clarity. Forexample, so-called halo implant regions are not depicted in thedrawings, as well as various layers or regions of silicon/germanium thatare typically found in high performance PMOS transistors. At the pointof fabrication depicted in FIG. 1A, the various structures of the device10 have been formed and a chemical mechanical polishing (CMP) processhas been performed to remove any materials above the sacrificial gateelectrode 15 (such as a protective cap layer (not shown) comprised ofsilicon nitride) so that at least the sacrificial gate electrode 15 maybe removed.

As shown in FIG. 1B, one or more etching processes are performed toremove the sacrificial gate electrode 15 and the sacrificial gateinsulation layer 14 to thereby define a gate cavity 20 where areplacement gate structure will subsequently be formed. Typically, thesacrificial gate insulation layer 14 is removed as part of thereplacement gate technique, as depicted herein. However, the sacrificialgate insulation layer 14 may not be removed in all applications.

Next, as shown in FIG. 1C, various layers of material that willconstitute a replacement gate structure 30 are formed in the gate cavity20. Even in cases where the sacrificial gate insulation layer 14 isintentionally removed, there will typically be a very thin native oxidelayer (not shown) that forms on the substrate 12 within the gate cavity20. The materials used for the replacement gate structures 30 for NMOSand PMOS devices are typically different. For example, the replacementgate structure 30 for an NMOS device may be comprised of a high-k gateinsulation layer 30A, such as hafnium oxide, having a thickness ofapproximately 2 nm, a first metal layer 30B (e.g., a layer of titaniumnitride with a thickness of about 1-2 nm that serves as a barrier layerto protect the high-k gate insulation layer 30A from reacting with thework function metal for the device), a second metal layer 30C—aso-called work function adjusting metal layer for the NMOS device—(e.g.,a layer of titanium-aluminum or titanium-aluminum-carbon with athickness of about 5 nm), a third metal layer 30D (e.g., a layer oftitanium nitride with a thickness of about 1-2 nm that serves to protectthe second metal layer 30C from oxidation and it also may function as anadhesion and nucleation layer for the later bulk deposition of tungstenor aluminum materials) and a bulk metal layer 30E, such as aluminum ortungsten. Ultimately, as shown in FIG. 1D, one or more CMP processes areperformed to remove excess portions of the gate insulation layer 30A,the first metal layer 30B, the second metal layer 30C, the third metallayer 30D and the bulk metal layer 30E positioned outside of the gatecavity 20 to thereby define the replacement gate structure 30 for anillustrative NMOS device. Typically, the replacement metal gatestructure 30 for a PMOS device does not include as many metal layers asdoes an NMOS device. For example, the gate structure 30 for a PMOSdevice may only include the high-k gate insulation layer 30A, a singlelayer of titanium nitride—the work function adjusting metal for the PMOSdevice—having a thickness of about 3-4 nm, and the bulk metal layer 30E.

As the gate length of transistor devices has decreased, the physicalsize of the gate cavity 20 has also decreased. Thus, it is becomingphysically difficult to fit all of the needed layers of material neededfor the replacement gate structure 30, particularly for NMOS devices dueto the greater number of layers of material that are typically used toform the gate structures for the NMOS devices, within the reduced-sizegate cavity. For example, as gate lengths continue to decrease, voids orseams may be formed as the various layers of material are deposited intothe gate cavity 20. Such voids or seams may result in devices thatperform at levels less than anticipated or, in some cases, the formationof devices that are simply not acceptable and have to be discarded.

The term “work function” (WF) is commonly used in the art ofsemiconductor design and manufacturing to refer to the minimum energyneeded to remove an electron from the surface of metal. The workfunction of a metal is typically a constant characteristic of that metalmaterial and it is usually measured in electron-volts (eV). In general,in CMOS integration schemes using a silicon substrate, a work functionmetal having a work function near the conduction band edge of silicon(about 4.0 eV) is necessary for NMOS type devices, while a differentwork function metal having a work function near the valance band edge ofsilicon (about 5.1-5.2 eV) is necessary for PMOS devices. Thus, in CMOSintegration schemes employing high-k gate dielectric materials, at leasttwo types of gate stacks are needed, i.e., a stack of suitable materialsthat satisfies the individual work function requirements for the PMOSdevices and a different stack of materials that satisfies the individualwork function requirements for the NMOS devices. As noted above, thegate stack for the PMOS devices provides an effective work functioncloser to the valence band edge of the material of the channel of thePMOS devices, and the gate stack for the NMOS devices provides aneffective work function closer to the conduction band edge of thematerial of the channel of the NMOS devices. Forming such differentlayer stacks for different devices is time consuming and involves manycomplex process operations.

The present disclosure is directed to various novel methods of forminggate structures for transistor devices for CMOS applications and variousnovel integrated circuit products that contain such transistor devicesthat may solve or reduce one or more of the problems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

Generally, the present disclosure is directed to various novel methodsof forming gate structures for transistor devices for CMOS applicationsand various novel integrated circuit products that contain suchtransistor devices. One illustrative integrated circuit productdisclosed herein includes, among other things, an NMOS transistor havinga gate structure comprised of an NMOS gate insulation layer comprised ofa high-k gate insulation material, a first NMOS metal layer comprised ofa first metal positioned on the NMOS gate insulation layer and a NMOSmetal silicide material positioned above the first NMOS metal layer,wherein the NMOS metal silicide material comprises a first amount ofatomic silicon. In this embodiment, the product also includes a PMOStransistor having a gate structure comprised of a PMOS gate insulationlayer comprised of the high-k gate insulation material, a first PMOSmetal layer comprised of the first metal positioned on the PMOS gateinsulation layer, and a PMOS metal silicide material positioned abovethe first PMOS metal layer, wherein the PMOS metal silicide materialcomprises a second amount of atomic silicon, and wherein the first andsecond amounts of atomic silicon are different.

Another illustrative integrated circuit product includes, among otherthings, an NMOS transistor having a gate structure comprised of an NMOSgate insulation layer comprised of a high-k gate insulation material, afirst NMOS metal layer comprised of a first metal positioned on the NMOSgate insulation layer, and a NMOS metal silicide material positionedabove the first NMOS metal layer, wherein the NMOS metal silicidematerial comprises 50-95% atomic silicon. In this embodiment, theintegrated circuit product also includes a PMOS transistor having a gatestructure comprised of a PMOS gate insulation layer comprised of thehigh-k gate insulation material, a first PMOS metal layer comprised ofthe first metal positioned on the PMOS gate insulation layer and a PMOSmetal silicide material positioned above the first PMOS metal layer,wherein the PMOS metal silicide material comprises 2-40% atomic silicon.

One illustrative method disclosed herein for forming replacement gatestructures for an NMOS transistor and a PMOS transistor includes, amongother things, performing at least one etching process to remove asacrificial gate structure for the NMOS transistor and a sacrificialgate structure for the PMOS transistor to thereby define an NMOS gatecavity and a PMOS gate cavity, depositing a gate insulation layer in theNMOS gate cavity and in the PMOS gate cavity, depositing a first metallayer on the gate insulation layer in the NMOS gate cavity and in thePMOS gate cavity, performing at least one process operation to form (1)an NMOS metal silicide material positioned above the first metal layerwithin the NMOS gate cavity, wherein the NMOS metal silicide materialcomprises a first amount of atomic silicon and (2) a PMOS metal silicidematerial positioned above the first metal layer within the PMOS gatecavity, wherein the PMOS metal silicide material comprises a secondamount of atomic silicon, and wherein the first and second amounts ofatomic silicon are different, and forming gate cap layers within theNMOS and PMOS gate cavities.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1A-1D depict one illustrative prior art method of forming a gatestructure of the transistors using a so-called “replacement gate”technique;

FIGS. 2A-2I depict one illustrative method disclosed herein for forminggate structures for transistor devices and an example of an integratedcircuit product that contain such transistor devices;

FIGS. 3A-3B depict various aspects of one method disclosed hereinwherein a metal silicide layer comprised of tungsten silicide has beenformed as part of the process of forming a gate structure for anillustrative transistor device;

FIGS. 4A-4H depict yet another illustrative method disclosed herein forforming gate structures for transistor devices and an example of anintegrated circuit product formed using CMOS technology;

FIGS. 5A-5E depict yet another illustrative method disclosed herein forforming gate structures for transistor devices and an example of anintegrated circuit product that contain such transistor devices; and

FIGS. 6A-6F depict yet another illustrative method disclosed herein forforming gate structures for transistor devices and an example of anintegrated circuit product formed using CMOS technology.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

The present disclosure is directed to various novel methods of forminggate structures for transistor devices for CMOS applications and variousnovel integrated circuit products that contain such transistor devices.As will be readily apparent to those skilled in the art upon a completereading of the present application, the methods disclosed herein may beemployed in manufacturing a variety of different devices, including, butnot limited to, logic devices, memory devices, etc. With reference tothe attached figures, various illustrative embodiments of the methodsand devices disclosed herein will now be described in more detail.

As will be appreciated by those skilled in the art after a completereading of the present application, the inventions disclosed herein maybe employed in forming integrated circuit products using planartransistor devices, as well as so-called 3D devices, such as FiNFETs, ora combination of such devices. For purposes of disclosure, referencewill be made to one illustrative process flow wherein the methodsdisclosed herein are performed to form an illustrative FinFET device. Inother embodiments, the methods disclosed herein may be employed tomanufacture integrated circuit products using CMOS technology to form aplurality of FinFET devices. However, the inventions disclosed hereinshould not be considered to be limited to such illustrative examples.For example, the inventions disclosed herein may be employed in forminga plurality of FinFET transistor devices or planar transistor devicesusing NMOS, PMOS or CMOS technology.

FIG. 2A is a simplified view of an illustrative integrated circuitproduct 100 at an early stage of manufacturing. An illustrativetransistor 104 will be formed in and above the semiconductor substrate102. So as not to obscure the inventions disclosed herein, an isolationregion that is formed in the substrate 102 to define an active regionwhere the transistor 104 will be formed is not depicted in the attacheddrawings. The transistor 104 may be either an N-type transistor or aP-type transistor. Additionally, various doped regions, e.g.,source/drain regions, halo implant regions, well regions and the like,are also not depicted in the attached drawings. The substrate 102 mayhave a variety of configurations, such as the depicted bulk siliconconfiguration. The substrate 102 may also have a silicon-on-insulator(SOI) configuration that includes a bulk silicon layer, a buriedinsulation layer and an active layer, wherein semiconductor devices areformed in and above the active layer. The substrate 102 may be made ofsilicon or it may be made of materials other than silicon. Thus, theterms “substrate” or “semiconductor substrate” should be understood tocover all semiconducting materials and all forms of such materials. Thecross-sectional view depicted in the attached figures is taken throughthe long axis of an illustrative fin 113 that is formed from thesubstrate 102. Stated another way, the cross-sectional views depicted inthe attached drawings are taken through the gate structures of thevarious transistors in a direction that corresponds to the gate lengthdirection of the transistors.

In the example disclosed herein, the transistor 104 will be formed usinga replacement gate technique. Accordingly, FIG. 2A depicts the product100 at a point in fabrication wherein a sacrificial gate structure 103has been formed above the substrate 102. As noted above, at this pointin the replacement gate process flow, source/drain regions (not shown)would have already been formed in the substrate 102 and an annealprocess would have been performed to activate the implanted dopantmaterials and repair any damage to the substrate 102 due to the variousion implantation processes that were performed. The sacrificial gatestructure 103 includes a sacrificial gate insulation layer 106 and adummy or sacrificial gate electrode 108. Also depicted are anillustrative sidewall spacer 112 and an illustrative gate cap layer 110.The various components and structures of the product 100 may be formedusing a variety of different materials and by performing a variety ofknown techniques. For example, the sacrificial gate insulation layer 106may be comprised of silicon dioxide, the sacrificial gate electrode 108may be comprised of polysilicon, and the sidewall spacer 112 and thegate cap layer 110 may be comprised of silicon nitride. The layers ofmaterial depicted in FIG. 2A, as well as the layers of materialsdescribed below, may be formed by any of a variety of different knowntechniques, e.g., a chemical vapor deposition (CVD) process, an atomiclayer deposition (ALD) process, a thermal growth process, physical vapordeposition (PVD), or plasma enhanced versions of such processes, etc.Also depicted in FIG. 2A is a layer of insulating material 114, e.g.,silicon dioxide, a low-k material (k value less than about 3.3), etc.,that was deposited above the product 100. In one embodiment, the layerof insulating material 114 may be a layer of silicon dioxide that isformed by performing a CVD process. The layer of insulating material 114may be formed to any desired thickness. FIG. 2A depicts the product 100after a planarization process has been performed on the layer ofinsulating material 114 such that the upper surface 114S of the layer ofinsulating material 114 is substantially even with the upper surface110S of the gate cap layer 110. Importantly, this planarization processexposes the upper surface 110S of the gate cap layer 110 such that itcan be removed. In one illustrative embodiment, the planarizationprocess may be a chemical mechanical planarization (CMP) process thatstops on the gate cap layer 110, or it may be a timed etch-back processthat removes the layer of insulating material 114 selectively relativeto the gate cap layer 110.

FIG. 2B depicts the product 100 after one or more wet or dry etchingprocesses were performed to remove the gate cap layer 110, thesacrificial gate electrode 108 and the sacrificial gate insulation layer106 to thereby define a gate cavity 116 where a replacement gatestructure will subsequently be formed for the transistor 104. Typically,the sacrificial gate insulation layer 106 is removed as part of thereplacement gate technique, as depicted herein. However, the sacrificialgate insulation layer 106 may not be removed in all applications. Evenin cases where the sacrificial gate insulation layer 106 isintentionally removed, there will typically be a very thin native oxidelayer (not shown) that forms on the substrate 102 within the gate cavity116.

FIG. 2C depicts the product after several process operations wereperformed. First, a pre-clean process was performed in an attempt toremove all foreign materials from within the gate cavity 116 prior toforming the various layers of material that will become part of thereplacement gate structure. Thereafter, a high-k (k value greater than10) gate insulation layer 118, such as hafnium oxide, having a thicknessof approximately 2 nm was initially deposited in the gate cavity 116 byperforming an ALD process.

Next, as shown in FIG. 2D, a first metal layer 120 (e.g., a layer oftitanium nitride with a thickness of about 1-5 nm) was formed on thehigh-k gate insulation layer 118 and within the gate cavity 116. Thefirst metal layer 120 is comprised of a metal that may serve as abarrier layer to protect the high-k gate insulation layer 118 during aso-called “reliability anneal” process that will be performed toincrease the reliability of the high-k gate insulation layer 118, asdescribed more fully below. In one example, the first metal layer 120may be formed by performing a plasma-enhanced physical vapor deposition(PVD) process. Next, a silicon-containing material layer (not shown),such as polysilicon or amorphous silicon, is blanket-deposited on theproduct 100 so as to over-fill the gate cavity 116. Thesilicon-containing material layer may be formed by performing, forexample, a CVD process. After the silicon-containing material layer isformed, an anneal process may be performed to increase the reliabilityof the high-k gate insulation layer 118. The parameters of such ananneal process are well known to those skilled in the art. Thesilicon-containing layer may then be removed by performing an etchingprocess. In some cases, the first metal layer 120 may remain in placewhile, in other applications, but typically, the first metal layer 120that was used in the reliability anneal of the high-k gate insulationlayer 118 will be removed (by selective etching relative to the high-kgate insulation layer 118) and a “new” first metal layer 120 will beformed on the high-k gate insulation layer 118. However, the presentapplication should be understood to cover both situations.

FIG. 2E depicts the product 100 in accordance with one illustrativeembodiment disclosed herein where a metal silicide deposition process121 is performed to directly deposit a metal silicide layer 122 on theproduct 100 so as to, in one embodiment, substantially over-fill thereaming portions of the gate cavity 116. In the depicted example, themetal silicide layer 122 is deposited on the first metal layer 120. Inother applications, another optional metal layer (indicated by thedashed line 123) that may act as an adhesion layer may be formed on thefirst metal layer 120 prior to forming the metal silicide layer 122.Whether or not such an adhesion layer is employed may vary upon thematerial selected for the first metal layer 120 and the composition ofthe metal silicide layer 122. So as not to obscure the presentlydisclosed inventions, the layer 123 will not be depicted in anysubsequent drawings.

In one illustrative embodiment, the metal silicide layer 122 may beformed by performing an ALD, a CVD or a PVD process (or plasma-enhancedversions of such processes), and it may be formed to any desiredthickness 122T (as measured above a substantially planar surface). Insome applications, the metal silicide layer 122 may be formed in such amanner such that few, if any, voids are present in the gate cavity 116.In other applications, due to the limited width of the gate cavity 116,when the metal silicide layer 122 is deposited, it may tend to“pinch-off” the gate cavity 116, thereby creating a void or seam in themetal silicide layer 122 within the cavity 116. In the case where such avoid is formed, the gate metal material that will be subsequently formed(as described more fully below) may fill all or a portion of such avoid. For purposes of disclosing the present inventions, the metalsilicide layer 122 will be depicted as having been formed in such amanner so as to result in a substantially void-free metal silicide layer122.

The metal silicide layer 122 may be comprised of any of a variety ofmetal silicide materials, e.g., tungsten silicide, hafnium silicide,tantalum silicide, titanium silicide, nickel-platinum silicide, cobaltsilicide, erbium silicide, molybdenum silicide, lanthanum silicide,yttrium silicide, ytterbium silicide, a silicide of a refractory metal,a silicide of a rare earth metal or a silicide of a transition metal,etc. The metal silicide layer 122 may also be deposited to any desiredthickness 122T, e.g., 1-7 nm. In one illustrative embodiment where themetal silicide layer 122 is comprised of tungsten silicide, it may beformed using WF₆ or WCl₆ and SiH₄ or Si₂H₆ as precursor gases at flowrates of about 10-5000 sccm and 10-5000 sccm, respectively, at atemperature that falls within the range of about 200-600° C. and at apressure that falls within the range of about 0.1-100 Torr. Of course,the process conditions can vary based upon, among other things, thedesign of the process chamber and the desired composition of the metalsilicide layer 122.

In the depicted example in FIG. 2E, the metal silicide layer 122 isshown as having the atomic silicon uniformly distributed throughout thethickness 122T of the metal silicide layer 122. In practice,concentration of the atomic silicon within the metal silicide may not beuniform. Moreover, in some applications, the parameters of thedeposition process 121 may be intentionally varied such that there is avariation in the amount of atomic silicon throughout the thickness 122Tof the metal silicide layer 122. In general, the ratio of metal tosilicon can be changed by controlling various process parameters. Forexample, the deposition process 121 may be controlled such that there isa higher concentration of atomic silicon in the metal silicide layer 122at the bottom surface 122B of the metal silicide layer 122, i.e., at theinterface with the first metal layer 120, than there is at the uppersurface 122U of the metal silicide layer 122. One illustrative way toachieve a metal silicide layer 122 with such a variation in atomicsilicon is by reducing the amount of silicon-containing precursors usedin the deposition process (either continuously or in a step-wisefashion) as the deposition process 121 proceeds. Of course, if desired,the deposition process 121 could be performed in such a manner thatthere is a higher concentration of atomic silicon in the metal silicidelayer 122 at the upper surface 122U of the metal silicide layer 122 thanthere is at the bottom surface 122B of the metal silicide layer 122.

The inventors have discovered that, by varying the amount of atomicsilicon in the metal silicide layer 122, the effective work function ofthe overall stack of the gate metals at the interface between the firstmetal layer 120 and the high-k gate insulation layer 118 may becontrolled or “tuned” to a desired level. FIGS. 3A-3B depict variousaspects of the process that may be performed to form the metal silicidelayer 122. FIG. 3A is a graph of the effective work function (EWF) ofthe overall gate stack of materials as a function of the atomicpercentage of silicon in an illustrative metal silicide layer 122comprised of a 5 nm thick tungsten silicide that is deposited on a firstmetal layer 120 comprised of titanium nitride (TiN) that is about 2 nmin thickness. In the illustrative example where the metal silicide layer122 is comprised of tungsten silicide, the effective work function of agate stack that includes such a tungsten silicide layer 122 may be tunedor adjusted to have effective work function values that fall within therange of about 4.4 eV to about 4.8 eV. Typically, work functionadjusting metals for use with N-type transistor devices, e.g., TiAlC,normally result in a gate stack that has an effective work function lessthan about 4.6 eV. On the other hand, work function adjusting metalscommonly used for P-type transistor devices typically result in a gatestack having an effective work function greater than about 4.8 eV. Thus,as will be recognized by those skilled in the art after a completereading of the present application, the methods and structures disclosedherein may be employed to form metal silicide layers 122 that can beindividually tailored to be used with N-type or P-type transistordevices.

In one particular application, the methods disclosed herein may beemployed in CMOS applications. For example, metal silicide layers 122that are intended to be used with N-type transistor devices may beformed with about 50-90% atomic silicon. In contrast, metal silicidelayers 122 that are intended to be used with P-type transistor devicesmay be formed with about 2-40% atomic silicon. The amount of siliconcontained in the metal silicide layer 122 may be controlled by, forexample, varying the amount of a silicon-containing precursor, such assilane, disilane, tri-silane, etc., that is used when depositing themetal silicide layer 122. Other illustrative techniques that may beemployed to control the amount of silicon contained in the metalsilicide layer 122 include, but are not limited to, controlling thetemperature of the deposition process, controlling the duration of timeduring which precursors are introduced into the process chamber, etc.The exact process parameters will need to be determined by experimentwith the exact process flow and materials used in each application. FIG.3B is a plot of the effective work function (vertical axis) of theoverall gate stack that includes the metal silicide layer 122 as afunction of the thickness (horizontal axis) of the metal silicide layer122 in the case where the metal silicide layer 122 is comprised oftungsten silicide. Additionally, in FIG. 3B, the amount of atomicsilicon present in the metal silicide layer 122 is at a constant levelof about 63%. As can be seen by the curve in FIG. 3B, the curve isfairly flat when the thickness of the metal silicide layer 122 is belowabout 0.3-0.5 nm, trends downward with increasing thickness of the metalsilicide layer 122, then begins to flatten out again when the thicknessof the metal silicide layer 122 reaches a value of about 3 nm. As can beseen from FIG. 3B, for a constant atomic percentage of silicon (about63%), the effective work function of the overall gate stack thatincludes the metal silicide layer 122 may be varied from about 4.85 eVto about 4.5 eV by changing the thickness of the metal silicide layer122 from about 0.1-5 nm, and saturates beyond about 5 nm.

In addition to some of the benefits described above, in at least someapplications, by using the metal silicide layer 122 disclosed herein,the resistance of the metals used in the final gate structure for thetransistor 104 may be greatly decreased relative to prior art transistorstructures. As one example, for a typical prior art N-type transistordevice, the work function adjusting metal employed in such a devicemight be titanium-aluminum-carbon (TiAlC) having a thickness of about2-10 nm. Such a layer of titanium-aluminum-carbon (TiAlC) was typicallypositioned between two layers of titanium nitride. A layer oftitanium-aluminum-carbon (TiAlC) typically has a resistivity value ofabout 2000 μohms-cm. Using the methods disclosed herein, an N-typetransistor device may be formed using the above-described metal silicidelayer 122 in lieu of the titanium-aluminum-carbon (TiAlC) layer (andwithout the capping titanium nitride layer as well in someapplications). Importantly, the metal silicide layer 122 disclosed mayhave a resistivity value of about 200 μohms-cm—approximately an order ofmagnitude less than that of titanium-aluminum-carbon (TiAlC)—a materialthat is frequently employed as a work function adjusting metal on N-typetransistor devices. Of course, such a dramatic change in resistancevalues may not be present in all situations, as it depends upon thematerials of construction that are the basis of the comparison. However,as will be appreciated by those skilled in the art after a completereading of the present application, such a reduction in the resistancevalue of at least some of the materials used in the gate structures oftransistor devices can provide significant advantages as it relates tothe design and manufacture of integrated circuit products.

FIG. 2F depicts the product 100 after several processing operations wereperformed on the device. In one embodiment, one or more CMP processeswere performed to remove the portions of the layers 118, 120 and 122positioned above the surface 114S of the layer of insulating material114 and outside of the gate cavity 116. Thereafter, one or more dry orwet etching process were performed on the high-k gate insulation layer118, the first metal layer 120 and the metal silicide layer 122 to forma recess 119 in the gate cavity 116. The depth of the recess 119 mayvary depending upon the particular application, e.g., about 10-20 nm. Insome applications, the CMP processes may be omitted and the structuredepicted in FIG. 2F may be achieved by simply performing one or moreetching processes.

FIG. 2G depicts the product 100 after a second metal layer 124 wasblanket-deposited on the product 100 so as to over-fill recess the 119in the gate cavity 116. The second metal layer 124 may be comprised of avariety of conductive materials, e.g., tungsten, aluminum, cobalt,nickel, etc., and it may be formed by performing, for example, a CVD orPVD process. The second metal layer 124 may be formed to any desiredthickness.

FIG. 2H depicts the product 100 after a dry or wet etching process wasperformed on the second metal layer 124 to thereby produce a recessedsecond metal layer 124R having a recessed upper surface that defines arecess 125. In one embodiment, the recessing process may be a timedetching process. In one illustrative example, the recessing process isperformed in such a manner that the depth of the recess 125 is about10-20 nm.

FIG. 2I depicts the product 100 after several process operations wereperformed. First, a layer of gate cap material, e.g., silicon nitride,was blanket-deposited above the product 100. Thereafter, a planarizationprocess was performed on the layer of gate cap material to therebydefine a gate cap layer 126 for the transistor 104. In one illustrativeembodiment, the planarization process may be a chemical mechanicalplanarization (CMP) process that stops on the layer of insulatingmaterial 114.

At this point in the process flow, the final gate structure 150 for thetransistor 104 has been formed. The gate cap layer 126 has also beenformed to protect the final gate structure 150. Using the methodsdisclosed herein, the stack of material layers for the final gatestructure 150 may be formed by depositing fewer layers of materialwithin the gate cavity 116, especially as it relates to N-type devices.This leaves significantly more room within the gate cavity 116 to formthe additional needed metal materials within the gate cavity 116. Moreimportantly, the methodologies disclosed herein are equally compatiblewith forming replacement gate structures for PMOS devices, as shownabove. Thus, the methods disclosed herein have significant value as itrelates to forming integrated circuit products using CMOS technology.Other benefits will be apparent to those skilled in the art after acomplete reading of the present application. At the point of fabricationdepicted in FIG. 2I, the integrated circuit product 100 may be completedby performing several traditional manufacturing processes, e.g., theformation of contacts to the source/drain regions of the device, theformation of various metallization layers for the product, etc.

FIGS. 4A-4H depict yet another illustrative method disclosed herein forforming gate structures for transistor devices and an example of anintegrated circuit product 100A that is formed using CMOS technology. Anillustrative NMOS transistor 104N and an illustrative PMOS transistor104P will be formed in and above the semiconductor substrate 102. In theexample disclosed herein, the transistors 104N, 104P will be formedusing a replacement gate technique. Accordingly, FIG. 4A depicts theproduct 100A at a point in fabrication wherein sacrificial gatestructures 103 have been formed above the substrate 102. As noted above,at this point in the replacement gate process flow, source/drain regions(not shown) would have already been formed in the substrate 102 and ananneal process would have been performed to activate the implanteddopant materials and repair any damage to the substrate 102 due to thevarious ion implantation processes that were performed. The sacrificialgates structures 103 include the above-described sacrificial gateinsulation layer 106 and dummy or sacrificial gate electrode 108. Alsodepicted are the above-described sidewall spacers 112, gate cap layers110 and layer of insulating material 114. At the point of fabricationdepicted in FIG. 4A, a planarization process has been performed on thelayer of insulating material 114 such that the upper surface 114S of thelayer of insulating material 114 is substantially even with the uppersurface 110S of the gate cap layers 110 so that they can be removed.

FIG. 4B depicts the product 100A after several process operations, e.g.,planarization and/or etching processes, were performed to remove thegate cap layers 110, the sacrificial gate electrodes 108 and thesacrificial gate insulation layers 106 to thereby define gate cavities116N, 116P where a replacement gate structure will subsequently beformed for the N-type transistor 104N and the P-type transistor 104P,respectively. Typically, the sacrificial gate insulation layers 106 areremoved as part of the replacement gate technique, as depicted herein.However, the sacrificial gate insulation layers 106 may not be removedin all applications. Even in cases where the sacrificial gate insulationlayers 106 are intentionally removed, there will typically be a verythin native oxide layer (not shown) that forms on the substrate 102within the gate cavities 116N, 116P.

FIG. 4C depicts the product 100A after several process operations wereperformed. First, a pre-clean process was performed in an attempt toremove all foreign materials from within the gate cavities 116N, 116Pprior to forming the various layers of material that will become part ofthe replacement gate structures. Thereafter, the above-described high-kgate insulation layer 118 was formed within the gate cavities 116N, 116Pand the first metal layer 120 was formed on the high-k gate insulationlayer 118. Next, after forming a layer of polysilicon or amorphoussilicon (not shown) above the first metal layer 120, the above-describedhigh-k reliability anneal process was performed. Then, the layer ofpolysilicon or amorphous silicon was removed. As noted above, the firstmetal layer 120 that was used during the reliability anneal process mayremain in place while, in other applications, the first metal layer 120that was used in the reliability anneal process may be removed andreplaced with a “new” first metal layer 120. Also depicted in FIG. 4C(in dashed lines) is the above-described optional adhesion layer 123that may be required or desired in some applications. As before, thelayer 123 will not be depicted in any subsequent drawings.

Using the methods described herein, the metal silicide layer 122described above may be tailored for either N-type or P-type devices,thus making it an attractive option for forming work function adjustinglayers in CMOS applications. Using the illustrative process flowdescribed herein, a metal silicide layer 122N that is tailored for theNMOS device 104N will be formed first. However, after a complete readingof the present application, those skilled in the art will appreciatethat a tailored metal silicide layer 122P that is tailored for the PMOSdevice could have been formed first if desired.

Accordingly, FIG. 4D depicts the product 100A after a metal silicidelayer 122N that has an atomic silicon content tailored for the NMOSdevice 104N is deposited on the product 100A so as to substantiallyover-fill both of the remaining portions of the gate cavities 116N,116P. In one illustrative embodiment, the metal silicide layer 122N maybe formed with about 50-95% atomic silicon. The metal silicide layer122N may be formed using the methods and materials described above withrespect to the metal silicide layer 122.

FIG. 4E depicts the product 100A after several process operations wereperformed. First, a patterned masking layer 141 was formed above theproduct 100A. The patterned masking layer 141 covers the NMOS regionwhile leaving the PMOS region exposed for further processing. In oneembodiment, the patterned masking layer 141 may be a patterned layer ofphotoresist material that may be formed using known photolithographytools and techniques or it may be a patterned hard mask layer, such as alayer of silicon nitride. Next, a dry or wet etching process wasperformed to remove the exposed portions of the metal silicide layer122N, thereby re-exposing some of the gate cavity 116P for the PMOStransistor 104P.

FIG. 4F depicts the product 100A after several process operations wereperformed. First, the patterned mask layer 141 was removed. Then, asecond metal silicide layer 122P that has an atomic silicon contenttailored for the PMOS device 104P was deposited on the product 100A soas to substantially over-fill the remaining portions of the gate cavity116P. In one illustrative embodiment, the metal silicide layer 122P maybe formed with about 2-40% atomic silicon. The metal silicide layer 122Pmay be formed using the methods and materials described above withrespect to the metal silicide layer 122. In general, the amount ofatomic silicon in the metal silicide layer 122N (for the NMOS device104N) will be greater than the amount of atomic silicon in the metalsilicide layer 122P (for the PMOS device 104P). Typically, the amount ofatomic silicon present in the metal silicide layer 122N for the NMOSdevice may be at least ten (10) atomic percent greater than the amountof atomic silicon present in the metal silicide layer 122P for the PMOSdevice. Also note that, using the methods disclosed herein to formtransistors in CMOS applications, the metal silicide layers 122N, 122Pmay not be made of the same metal silicide, although that situation mayoccur in some applications.

FIG. 4G depicts the product 100A after one or more planarizationprocesses have been performed to remove the portions of the metalsilicide layers 122N, 122P, the first metal layer 120 and the high-kgate insulation layer 118 that are positioned above the surface 114S ofthe layer of insulating material 114 and outside of the gate cavities116N, 116P. The structure depicted in FIG. 4G may be achieved byperforming one or more CMP and/or etching processes in any of a varietyof different processing sequences.

FIG. 4H depicts the product 100A after the processing sequence describedabove in connection with FIGS. 2G-2I was performed to result in theformation of the second metal layer 124R and the gate cap layer 126 asdepicted in the drawing. At this point in the process flow, the finalgate structures 150N, 150P for the transistors 104N, 104P, respectively,have been formed. At the point of fabrication depicted in FIG. 4H, theintegrated circuit product 100A may be completed by performing severaltraditional manufacturing processes, e.g., the formation of contacts tothe source/drain regions of the device, the formation of variousmetallization layers for the product, etc.

FIGS. 5A-5E depict yet another illustrative method disclosed herein forforming a gate structure for a transistor device 105 and an example ofan integrated circuit product 101 that contains such a transistor. Inthe example disclosed herein, the transistor 105 will be formed using areplacement gate technique. FIG. 5A depicts the product 101 at a pointin fabrication that approximately corresponds to that depicted in FIG.2D, i.e., the sacrificial gate structure of the transistor 105 has beenremoved and the above-described high-k gate insulation layer 118 wasformed within the gate cavity 116 and the first metal layer 120 wasformed on the high-k gate insulation layer 118. The above-describedhigh-k reliability anneal process would have also been performed at thispoint in the process flow. As noted above, the first metal layer 120depicted in FIG. 5A may have been used in the reliability anneal of thehigh-k gate insulation layer 118 or it may be a “new” first metal layer120. Also depicted in FIG. 5A (in dashed lines) is the above-describedoptional adhesion layer 123 that may be required or desired in someapplications. As before, the layer 123 will not be depicted in anysubsequent drawings.

FIG. 5B depicts the product 101 at a point in fabrication wherein anillustrative metal layer 145 is formed above the product 101. In oneillustrative embodiment, the metal layer 145 may be comprised of asingle layer of metal or multiple layers of metal, such as theillustrative first metal layer 145-1 (depicted in dashed lines) and asecond layer of metal 145-2 formed thereabove. The number of such metallayers may vary depending upon the particular application. For ease ofreference, the situation where multiple layers of metal may be formedabove the first metal layer 120 will not be depicted in the subsequentdrawings. The metal layer(s) 145 may be comprised of any of a variety ofmetals, e.g., tungsten, hafnium, tantalum, titanium, nickel, platinum, arefractory metal or a transition metal, or combinations of suchmaterials, etc. The metal layer(s) 145 may also be deposited to anydesired thickness 145T, e.g., 10-300 nm. In some applications, the metallayer(s) 145 may be formed in such a manner such that few, if any, voidsare present in the cavity 116. In other applications, due to the limitedwidth of the gate cavity 116, when the metal layer(s) 145 is formed, itmay tend to “pinch-off” the gate cavity 116, thereby creating a void orseam in the metal layer(s) 145 within the cavity 116. In the case wheresuch a void is formed, the gate metal material that will be subsequentlyformed (as described more fully below) may fill all or a portion of sucha void. For purposes of disclosing the present inventions, the metallayer(s) 145 will be depicted as having been formed in such a manner soas to result in a substantially void-free metal layer(s) 145.

Next, as shown in FIG. 5C, one or more process operations 147 will beperformed on the metal layer(s) 145 to convert all or a portion of themetal layer 145 into a metal silicide layer(s) 149. In general, theprocess operation 147 involves introducing atomic silicon in to themetal layer(s) 145. In the case where multiple layers of metal areformed, e.g., metal layers 145-1 and 145-2, separate process operations147 may be performed after each individual metal layer is formed or theprocess operation 147 may be performed after all of the multiple metallayers 145 (e.g., the layers 145-1 and 145-2) are formed. In the casewhere multiple layers of material are formed, the multiple layers ofmaterial may all be comprised of the same metal or they may be comprisedof different metals. Moreover, in the case where multiple layers ofmetal are formed, the parameters of individual process operations 147that are performed after the formation of each layer of metal may bedifferent as well, e.g., the amount of atomic silicon introduced duringeach individual process operation 147 may be different.

In one illustrative embodiment, the process operation 147 may be aplasma treatment process or a thermal treatment process performed in aprocess ambient comprised of a silicon-containing precursor. Forexample, a silicon-containing precursor such as silane, disilane,tri-silane, etc. may be introduced into a process chamber (not shown) ata flow rate of about 5-3000 sccm. Of course, the process conditions canvary based upon, among other things, the design of the process chamberand the desired composition of the metal silicide layer(s) 149.

In the case of a plasma-based process operation 147, the processoperation 147 may be performed at a temperature that falls within therange of about 25-1000° C. and at a pressure that falls within the rangeof about 0.1-100 Torr. Such a plasma-based process operation may beperformed for a duration of about 0.1-1000 seconds, depending upon thethickness of the metal layer(s) 145. The plasma power may fall withinthe range of about 10-10,000 W and the frequency may fall within therange of about 100 kHz-45 MHz. Of course, the process conditions canvary based upon, among other things, the design of the process chamberand the desired composition of the metal silicide layer(s) 149.

In another example, the process operation 147 may be a thermal treatmentprocess operation that is performed in a silicon-containing processambient that results in the formation of the metal silicide layer 149.In one embodiment, such a thermal treatment process may be performed ata temperature that falls within the range of about 200-1100° C. and at apressures that falls within the range of about 0.1-760 Torr.

In the depicted example in FIG. 5C, the metal silicide layer 149 isshown as having the atomic silicon uniformly distributed throughout thethickness of the metal silicide layer 149. In practice, the depth ofpenetration of the atomic silicon that is introduced by way of theprocess operation 147 may vary depending upon the particularapplication, i.e., atomic silicon may not penetrate the entire thicknessof the metal layer(s) 145. In practice, the concentration of the atomicsilicon within the metal silicide layer 149 may not be uniform.Moreover, in some applications, the parameters of the processoperation(s) 147 may be intentionally varied such that there is avariation in the amount of atomic silicon throughout the thickness ofthe metal silicide layer 149. For example, the process operation(s) 147may be controlled such that there is a higher concentration of atomicsilicon in the metal silicide layer 149 at the bottom surface 149B ofthe metal silicide layer 149, i.e., at the interface with the firstmetal layer 120, than there is at the upper surface 149U of the metalsilicide layer 149. One way to obtain a metal silicide layer 149 withsuch a variation in atomic silicon involves reducing the amount ofsilicon-containing precursors used in the process operation(s) 147(either continuously or in a step-wise fashion) as the processoperation(s) 147 proceeds. Of course, if desired, the processoperation(s) 147 could be performed in such a manner that there is ahigher concentration of atomic silicon in the metal silicide layer 149at the upper surface 149U of the metal silicide layer 149 than there isat the bottom surface 149B of the metal silicide layer 122. Otherillustrative techniques that may be employed to control the amount ofsilicon contained in the metal silicide layer 149 include, but are notlimited to, controlling the temperature of the process operation 147,controlling the duration of time during which precursors are introducedinto the process chamber, etc.

The inventors have discovered that, by varying the amount of silicon inthe metal silicide layer(s) 149, the effective work function (EWF) ofthe overall gate stack that includes the metal silicide layer 149 may becontrolled or “tuned” to a desired level. The data set forth in FIGS.3A-3B apply equally to this aspect of the presently disclosedinventions. Thus, using the methods described herein, the metal silicidelayer 149 described above may be tailored for either N-type or P-typedevices, thus making it an attractive option for, among other things,forming work function adjusting layers in CMOS applications. Theinventors have also discovered that annealing in inert atmospheresubsequent to the metal silicide deposition may reduce resistivity ofthe metal gate without having a major impact on the effective workfunction of the overall gate stack. An example of this includes atungsten silicide system. The annealing process can be done at 250-1000°C., although higher temperature anneals may adversely impact dopantprofiles. In one embodiment, such annealing may be performed in an argonenvironment, although other gases, such as N₂, He, H₂, etc., can also beused. In one embodiment, the pressure during such an anneal process mayfall within the range of about 100 mT-760 Torr.

FIG. 5D depicts the product 101 after one or more planarizationprocesses have been performed to remove the portions of the metalsilicide layer(s) 149, the first metal layer 120 and the high-k gateinsulation layer 118 that are positioned above the surface 114S of thelayer of insulating material 114 and outside of the gate cavity 116. Thestructure depicted in FIG. 5D may be achieved by performing one or moreCMP and/or etching processes in any of a variety of different processingsequences.

FIG. 5E depicts the product 101 after the processing sequence describedabove in connection with FIGS. 2G-2I was performed to result in theformation of the second metal layer 124R and the gate cap layer 126 asdepicted in the drawing. At this point in the process flow, the finalgate structure 160 for the transistor 105 has formed. At the point offabrication depicted in FIG. 5E, the integrated circuit product 101 maybe completed by performing several traditional manufacturing processes,e.g., the formation of contacts to the source/drain regions of thedevice, the formation of various metallization layers for the product,etc.

FIGS. 6A-6F depict yet another illustrative method disclosed herein forforming gate structures for transistor devices and an example of anintegrated circuit product 101A that is formed using CMOS technology.Accordingly, FIG. 6A depicts the product 101A at a point in fabricationthat approximately corresponds to that depicted in FIG. 4C, i.e., thesacrificial gate structures of the transistors 104N, 104P have beenremoved and the above-described high-k gate insulation layer 118 wasformed within the gate cavities 116N, 116P and the first metal layer 120was formed on the high-k gate insulation layer 118. The above-describedhigh-k reliability anneal process would have also been performed at thispoint in the process flow. As noted above, the first metal layer 120depicted in FIG. 6A may have been used in the reliability anneal of thehigh-k gate insulation layer 118 or it may be a “new” first metal layer120. Also depicted in FIG. 6A (in dashed lines) is the above-describedoptional adhesion layer 123 that may be required or desired in someapplications. As before, the layer 123 will not be depicted in anysubsequent drawings.

FIG. 6B depicts the product 101A after the above-described metallayer(s) 145 have been formed above the product 101A so as tosubstantially over-fill the gate cavities 116N, 116P. As noted above,the metal layer(s) 145 may be comprised of a single layer of metal ormultiple layers of metal.

Typically, when processing is completed, the metal silicide workfunction adjusting material for the PMOS device 104P will have a lowerrelative concentration of atomic silicon as compared to the amount ofatomic silicon that is present in the metal silicide work functionadjusting material for the NMOS device 104N. Thus, as shown in FIG. 6C,in one illustrative process flow, a first process operation 147-1 may beperformed to introduce an amount of atomic silicon into the entire metallayer 145 that corresponds to the lesser amount of atomic silicon usedfor the metal silicide work function adjusting metal silicide layer 149Pof the PMOS transistor 104P. In one illustrative embodiment, the firstprocess operation 147-1 may be performed such that the metal silicidelayer 149P may be formed with about 2-40% atomic silicon. The processoperation 147-1 may be any of the process operations 147 describedabove.

FIG. 6D depicts the product 101A after several process operations wereperformed. First, a patterned masking layer 151 was formed above theproduct 101A. The patterned masking layer 151 covers the PMOS regionwhile leaving the NMOS region exposed for further processing, i.e.,portions of the metal silicide layer 149 above the NMOS region areexposed for further processing. In one embodiment, the patterned maskinglayer 151 may be a patterned layer of photoresist material that may beformed using known photolithography tools and techniques or it may be apatterned hard mask layer, such as a layer of silicon nitride. Next, asecond process operation 147-2 is performed on the exposed portions ofthe metal silicide layer 149P so as to thereby effectively increase theamount of atomic silicon in the metal silicide layer 149P and therebyconvert it into a metal silicide layer 149N that has an atomic siliconcontent tailored for the NMOS device 104N. In one illustrativeembodiment, the process operations 147-1 and 147-2 are designed suchthat the metal silicide layer 149N may be formed with about 40-95%atomic silicon when all processing is completed. The process operation147-2 may be any of the process operations 147 described above.

FIG. 6E depicts the product 101A after several process operations wereperformed. First, the patterned mask layer 151 was removed. Then, one ormore planarization processes were performed to remove the portions ofthe metal silicide layers 149N, 149P, the first metal layer 120 and thehigh-k gate insulation layer 118 that are positioned above the surface114S of the layer of insulating material 114 and outside of the gatecavities 116N, 116P. The structure depicted in FIG. 6E may be achievedby performing one or more CMP and/or etching processes in any of avariety of different processing sequences.

FIG. 6F depicts the product 101A after the processing sequence describedabove in connection with FIGS. 2G-2I was performed to result in theformation of the second metal layer 124R and the gate cap layers 126 asdepicted in the drawing. At this point in the process flow, the finalgate structures 160N, 160P for the transistors 104N, 104P, respectively,have been formed. At the point of fabrication depicted in FIG. 6F, theintegrated circuit product 101A may be completed by performing severaltraditional manufacturing processes, e.g., the formation of contacts tothe source/drain regions of the device, the formation of variousmetallization layers for the product, etc.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Note that the use of terms, such as “first,” “second,”“third” or “fourth” to describe various processes or structures in thisspecification and in the attached claims is only used as a shorthandreference to such steps/structures and does not necessarily imply thatsuch steps/structures are performed/formed in that ordered sequence. Ofcourse, depending upon the exact claim language, an ordered sequence ofsuch processes may or may not be required. Accordingly, the protectionsought herein is as set forth in the claims below.

What is claimed:
 1. A method of forming replacement gate structures foran NMOS transistor and a PMOS transistor, comprising: performing atleast one etching process to remove a sacrificial gate structure forsaid NMOS transistor and a sacrificial gate structure for said PMOStransistor to thereby define an NMOS gate cavity and a PMOS gate cavity;depositing a gate insulation layer in said NMOS gate cavity and in saidPMOS gate cavity; depositing a first metal layer on said gate insulationlayer in said NMOS gate cavity and in said PMOS gate cavity; performingat least one process operation to form: an NMOS metal silicide materialpositioned above said first metal layer within said NMOS gate cavity,said NMOS metal silicide material comprising a first amount of atomicsilicon; and a PMOS metal silicide material positioned above said firstmetal layer within said PMOS gate cavity, said PMOS metal silicidematerial comprising a second amount of atomic silicon, wherein saidfirst and second amounts of atomic silicon are different; after formingsaid NMOS and PMOS metal silicide materials in said respective NMOS andPMOS gate cavities, performing at least one etching process to remove aportion of at least said respective NMOS and PMOS metal silicidematerials so as to form a recess in each of said respective NMOS andPMOS gate cavities; and forming respective gate cap layers within saidrecesses formed in said NMOS and PMOS gate cavities.
 2. The method ofclaim 1, wherein performing said at least one process operationcomprises: performing at least one first silicide deposition process todeposit said NMOS metal silicide material in at least said NMOS gatecavity; and performing at least one second silicide deposition processto deposit said PMOS metal silicide material in at least said PMOS gatecavity.
 3. The method of claim 1, wherein performing said at least oneprocess operation comprises: depositing at least one second layer ofmetal above said first metal layer in said NMOS gate cavity and in saidPMOS gate cavity; and introducing atomic silicon into said at least onesecond metal layer so as to covert at least a portion of said at leastone second metal layer into one of said NMOS metal silicide material orsaid PMOS metal silicide material.
 4. The method of claim 3, wherein thestep of introducing silicon into said at least one second layer of metalcomprises performing one of a plasma process operation or a thermaltreatment process operation on said at least one second metal layer in asilicon-containing process ambient.
 5. The method of claim 4, whereinperforming said plasma process operation comprises introducing asilicon-containing precursor into a process chamber at a flow rate ofabout 5-3000 sccm and performing said plasma process operation at atemperature that falls within the range of 25-1000° C., at a pressurethat falls within the range of 0.1-100 Torr, for a duration that fallswith the range of 0.1-1000 seconds, using a plasma power setting thatfalls within the range of 10-10,000 W and a frequency setting that fallswithin the range of 100 kHz-45 MHz.
 6. The method of claim 4, whereinperforming said thermal process operation comprises introducing asilicon-containing precursor into a process chamber at a flow rate ofabout 5-3000 sccm and performing said thermal process operation at atemperature that falls within the range of 200-1100° C. and at apressures that falls within the range of 0.1-760 Torr.
 7. The method ofclaim 1, wherein said NMOS metal silicide material and said PMOS metalsilicide material are comprised of the same metal silicide material. 8.The method of claim 1, wherein said NMOS metal silicide material andsaid PMOS metal silicide material are comprised of different metalsilicide materials.
 9. The method of claim 1, wherein the differencebetween said first and second amounts of atomic silicon is at least 10atomic percent.
 10. The method of claim 1, wherein said NMOS metalsilicide material comprises 50-95% atomic silicon.
 11. The method ofclaim 1, wherein said PMOS metal silicide material comprises 2-40%atomic silicon.
 12. The method of claim 1, wherein said gate insulationlayer is formed in each of said NMOS and PMOS gate cavities afterremoving said sacrificial gate structures for said respective NMOS andPMOS transistors.
 13. The method of claim 1, wherein said gateinsulation layer formed in at least one of said NMOS and PMOS gatecavities is formed so as to cover an entirety of bottom and sidewallsurfaces of a respective one of said NMOS and PMOS gate cavities.
 14. Amethod of forming replacement gate structures for an NMOS transistor anda PMOS transistor, the method comprising: performing at least oneetching process to remove a sacrificial gate structure for said NMOStransistor and a sacrificial gate structure for said PMOS transistor tothereby define an NMOS gate cavity and a PMOS gate cavity; afterremoving said sacrificial gate structures for said NMOS and said PMOStransistors, depositing a gate insulation layer in said NMOS gate cavityand in said PMOS gate cavity; depositing a first metal layer on saidgate insulation layer in said NMOS gate cavity and in said PMOS gatecavity; depositing a first metal silicide material above said firstmetal layer within said NMOS gate cavity, said first metal silicidematerial comprising a first amount of atomic silicon; depositing asecond metal silicide material above said first metal layer within saidPMOS gate cavity, said second metal silicide material comprising asecond amount of atomic silicon, wherein said first amount of atomicsilicon is different than said second amount of atomic silicon; afterdepositing said first and second metal silicide materials in saidrespective NMOS and PMOS gate cavities, performing at least one etchingprocess to remove a portion of at least said respective first and secondmetal silicide materials so as to form a recess in each of saidrespective NMOS and PMOS gate cavities; and forming respective gate caplayers within said recesses formed in said NMOS and PMOS gate cavities.15. The method of claim 14, wherein after depositing said first metalsilicide material in said NMOS gate cavity, said gate insulation layer,said first metal layer, and said first metal silicide materialsubstantially completely fill said NMOS gate cavity, and wherein afterdepositing said second metal silicide material in said PMOS gate cavity,said gate insulation layer, said first metal layer, and said secondmetal silicide material substantially completely fill said PMOS gatecavity.
 16. The method of claim 14, further comprising, prior to formingsaid respective gate cap layers, forming a second metal layer in each ofsaid respective recesses and thereafter forming said respective gate caplayers above said respective second metal layers.
 17. The method ofclaim 14, wherein said first metal silicide material and said secondmetal silicide material are comprised of different metal silicidematerials.
 18. The method of claim 14, wherein the difference betweensaid first and second amounts of atomic silicon is at least 10 atomicpercent.
 19. The method of claim 14, wherein said first metal silicidematerial comprises 50-95% atomic silicon.
 20. The method of claim 14,wherein said second metal silicide material comprises 2-40% atomicsilicon.
 21. A method of forming a replacement gate structure for atransistor, the method comprising: performing at least one etchingprocess to remove a sacrificial gate structure for said transistor so asto thereby define a gate cavity; after removing said sacrificial gatestructure, depositing a gate insulation layer in said gate cavity;depositing a first metal layer on said gate insulation layer in saidgate cavity; depositing a metal silicide material layer above said firstmetal layer within said gate cavity so that a bottom surface of saidmetal silicide material layer adjacent to said first metal layer has afirst concentration of atomic silicon and a top surface of said metalsilicide material layer opposite of said bottom surface has a secondconcentration of atomic silicon that is different than said firstconcentration; and forming a gate cap layer within said gate cavity. 22.The method of claim 21, wherein depositing said metal silicide materialhaving said first concentration of atomic silicon at said bottom surfaceof said metal silicide material layer and said second concentration ofatomic silicon at said top surface of said metal silicide material layercomprises adjusting, during a material deposition process, an amount ofsilicon-containing precursor gas in a deposition ambient used to depositsaid metal silicide material layer.
 23. The method of claim 21, furthercomprising performing at least one etch process to remove a portion ofat least said metal silicide material layer so as to form a recess insaid gate cavity, depositing a second metal layer in said recess, andforming said gate cap layer in said recess and above said second metallayer.
 24. The method of claim 21, further comprising, prior todepositing said metal silicide material layer, forming an adhesion layerabove said first metal layer within said gate cavity, wherein said metalsilicide layer is formed above said adhesion layer.